1. Field of the Invention
The present invention relates to using a differential signal overlay on an existing transmitted video signal for coding and transmission of a progressive video signal to a display.
2. Background Art
Moving images can be shown on televisions and other displays by successively displaying a number of still pictures. The rapid succession of images allows slight changes in movement of the pictures to be captured and shown in a smooth manner. The picture motion appears smoother if each of the pictures, commonly referred to as frames, are successively displayed at a rate faster than human perception, i.e., the movement appears smoother if the frames are displayed at a regular rate of at least 1/30th of a second apart or 30 frames per second.
The resolution at which the frames are displayed can vary depending on the capabilities of the display system and the encoding of the pictures. One resolution measurement is based on the number of vertical and horizontal lines of pixels that the display can support. One increasingly popular display resolution is 1080p which is used in High Definition (HD) signals and HD sets that are capable of handling this display format. As HD industry increasingly penetrates the television market, 1080p will become a common display format. Displays having capabilities to support 1080p are capable of displaying a picture of 1,920 horizontal pixels/line by 1,080 vertical pixel lines (full frame, total of 2,073,600 pixels) every 1/60th of a second. The 1080p level of resolution is considered to be progressive since a full frame is displayed every 1/60th of a second, i.e., such that all pixels of frame are display at one instance in time.
Another common signal and display resolution is 1080i (1920×1080 pixels at 30 frames per second). Signals and displays having capabilities to support 1080i resolution are capable of displaying every other vertical line of a picture such that the picture includes 1,920 horizontal pixels/line by 540 vertical pixel lines (half frame, total of 1,036,800 pixels) every 1/60th of a second. The other half of the picture is shown immediately after the first part of the picture, at the same rate and resolution, such that a perceived full frame is displayed every 1/30th of a second. The 1080i level of resolution is considered to be interlaced since alternating half frames (fields) are displayed every 1/60th of a second.
To facilitate transmitting the pictures, the pictures may be individually encoded and compressed. Any number of methodologies and standards are available for the video compression. Moving Picture Experts Group (MPEG) is one commonly used compression standard. Like many compression standards, MPEG breaks each frame into a number of blocks (macroblocks) or other units to facilitate transmitting the signal. The blocks may be separately compressed or omitted from transmission depending on the pictures included and the associated compression/transmission technique. The blocks are then reassembled for display in a process that predicts the location of a block for a current frame based on the location of a block in a reference or preceding frame.
Motion vectors may be associated with each block to facilitate predicting movement, and ultimately reconstructing the blocks. Motion vectors may be essential in many compression methodologies to provide a temporal component to compression. Motion vectors can be used to facilitate predicting the frame-to-frame location of macroblocks. This can be done temporally by aligning presentation timecode and then spatially by alignment of macroblocks at corresponding indexes or corresponding locations.